1. Field of the Invention
The present invention relates to a host device and a memory system, for example, a memory system having a NAND flash memory and a controller for controlling the memory, and a host device in which the memory system is inserted.
2. Description of the Related Art
At present, a memory system typified by a memory card using a nonvolatile semiconductor memory such as a flash memory is used as recording media for music data and video data. A typical example of the flash memory used in the memory system includes a NAND flash memory.
In the NAND flash memory, writing is performed in units called pages constituted by a plurality of bits. Erasing is performed in only units called blocks constituted by a plurality of pages. For this reason, when data stored in a block is partially rewritten, new data to be rewritten must be written in a new block from which data is erased, and unrewritable data must be copied from an old block including old data (rewritten with the new data) into the new block.
This process is called “moving write (victim copy)”. Since this “moving write” accompanies an operation of copying unrewritable data, overheads considerably increase when the “moving write” frequently occurs.
A file allocation table (FAT) file system is used as a file system to manage data stored in a storage medium. The FAT file system allocates data to clusters (units of write areas used by the file system to manage allocation of the data to the clusters by a table called FAT. The FAT file system is a file system based on a medium, such as a hard disk, on which data can be rapidly rewritten at random. The random write is a scheme in which data is written in an idle cluster at random independently of an address of a cluster.
In the FAT file system, each time file data (real data) constituting a file is rewritten, updating of management data such as FAT occurs. For this reason, when the FAT file system is employed as a file system for managing a NAND flash memory, “moving write” occurs each time file data is rewritten, so that a file writing speed decreases.
In the future, as the NAND flash memory is anticipated to increase in capacity, so is the size of a block. As a result, this is expected to exacerbate an adverse effect such as an increase in processing time required for “moving write” or the like.
In order to cope with a defect caused by a combination between a NAND flash memory and a FAT file system, it is proposed that an incremental write file system, such as a universal disc format (UDF), is used in a host device (Jpn. Pat. Appln. KOKAI Publication No. 2006-040264).
Use of the incremental write file system enables data to be efficiently written in a memory system using a NAND flash memory.
However, the incremental write file system is not compatible with the FAT file system. Furthermore, a new file system must be developed for and mounted on the host device. For this reason, the manufacturer of the host device is forced to bear the burden.